For me, the most likely piece of bad info is what the SA is telling you...wait for them to put it in writing and talk to the tech before you drive off, if you want the real story....

A

ard, you hit it right on the money . . . this was a case of comical mis-communication! Over the phone I heard the SA telling me they need to replace the "knock" sensor . . . what he actually said was "NOx" sensor! Now that makes a whole lot more sense! Agrees with the code my scanner read.

I met with the tech and he told me the codes they read (see attached) required them to replace the NOx sensors. He didn't think the SCR Mixer replacement and this sensor going bad was connected, just a coincidence - at least that was his best guess.

He has no idea why my fuel mileage improved by nearly 20% (from ~22.5% to over 27 mpg!). On my way back from the Dealer my mpg was about 24+ mpg (mostly hwy) . . . still higher than what I saw after the initial EGR valve replacement and associated re-programming. I will keep an eye on the mpg for the next several weeks and see where it finally settles. Since mpg is moving in the positive direction I am not complaining!